Various methods are known for protecting an audio amplifier from transient effects. As an example, Morris , Jr. et al. in U.S. Pat. No. 5,224,169 describes a system including stereo amplifiers, each supplied with dual supply voltages (+V and -V). A detector, coupled to the amplifier outputs, senses the amplifier output voltage and turns off the positive and negative supplies if sustained DC is present or if either supply fails. Brief DC transients (i.e., not "sustained") which may accompany the input signal may not be sensed. Lendaro, in U.S. Pat. No. 5,157,353 describes a protection circuit wherein the dual power supplies of an operational amplifier are provided with "slow start" circuitry which limits the rate of change of the supply voltages to suppress turn-on/turn-off transients. There is no provision, however, for suppressing transients which may accompany the input signal.
Other examples of amplifier protection circuits are described, for example, by Griffis in U.S. Pat. No. 4,405,948 in which supply voltage transients are detected and used for reducing the gain of a variable gain amplifier preceding an audio amplifier. In U.S. Pat. No. 5,199,079 Anderson et al. describe an arrangement including an amplifier having bias and supply voltages obtained from diode isolated filters that reduce the voltages slowly when the main voltage supply is de-energized.